Generally, printed material contains both pictorial (i.e. graphic) and alphanumeric (i.e., literal) components (the latter including drawing components), each of which is treated separately in a conventional process of photomechanics. Conventionally, both components are subsequently combined to form a complete reproduced image prior to the process of producing a press plate. However, this procedure is complicated and thus requires and consumes excessive quantities of time.
There has thus been recently developed a new type of image reproducing system. The newly developed system, a so-called "full-page make up system" or "total (lay-out) scanner" is being put to practical use in various fields. This system provides a scanner which utilizes a method of distributing pictorial and alpha-numeric components into desired positions by means of an all-electronic approach to the photomechanical process.
In the electronic approach, the graphic and literal components are input as signals to resepective input devices. The signals are then separately processed, since each component signal has a distinctive data structure. Furthermore, the literal data signal is converted into a raster-scanned data signal which is identical to that of the graphic data in order to be output simultaneously therewith by a recording device.
Of course, the literal data can be obtained as raster-scanned data from scanning of block copy which is preliminarily laid out in a desired formation. At any rate, in the prior art it is difficult to record both the graphic and literal components of the data simultaneously.
The difficulty arises not only because literal components require a higher resolution (smaller pixels), but also because graphic components are required to be variably recorded as functions of a halftone dot scale thereof (depending on the number of lines in a screen ruling) on request when recorded with halftone screens.
One prior art method for resolving this problem includes the steps of setting a scale of several graphic pixels for each of the literal pixels, and scanning a photosensitive material for recordng thereon, the scan having a predetermined number of lines with respect to that of graphic pixels. In said method multiple beam components, each of which can be individually controlled, may be arranged to form a line across the width of a scanning line (see, for example, U.S. patent application Ser. No. 390373). However, the above method is defective in having a reduced capacity for responding to a request for variation of the number of screen ruling lines.
Particularly, the setting of a desired number of screen ruling lines is a difficult task when the number is to be varied. Additionally, in order to maintain an integer proportional relation between literal and graphic pixels, there must be a sufficient number of beam components to cope with the requirement for a change in the number of said beam components due to variation in screen ruling, which results in a more expensive system.
Another method discloses the provision of separate scanning heads for graphic pixels and for literal pixels, the heads being used for recording (or exposing) the two types of pixels sequentially-e.g., first recording all the graphic pixels and thereafter recording all the literal pixels. This approach, however, requires performance of two whole scans by the heads. Although this is a reasonable approach for providing different recording beams having the respective appropriate diameters, the resulting exposure (or recording) time is doubled compared to that of simultaneous exposing.